| Summary: | Introduction: High-risk MDS & AML are the result of malignant transformation of an immature hematopoietic precursor. Venetoclax (Ven) is a selective inhibitor of the anti-apoptotic BCL2 protein that is FDA approved for the treatment of AML, despite which, the overall cure rates in HR-MDS and AML are dismal. Signal transducer and activator of transcription 3 (STAT3) is de-methylation and overexpression in MDS & AML stem cells. It is associated with an adverse prognosis in a large cohort of patients. We have also demonstrated that STAT3 controls several important leukemic drivers such as the anti-apoptotic protein MCL1, which is the central mechanism of venetoclax resistance. Methods: Ven resistant AML cell lines (MOLM-13, MV-4-11) demonstrated an increased expression of STAT3/ Phospho-STAT3 and the down-stream effector MCL1 when compared to parental cell lines. Data from > 90 AML patients treated with prior venetoclax show that high expression of STAT3 correlated with worse overall survival and remission duration. Results: A clinical degrader of STAT3 resulted in degradation of STAT3 in both parental and ven resistant cancer cell lines. STAT3 degradation also resulted in increased apoptosis in parental & Ven resistant MOLM-13 cell line. In primary patient colony assays, there was increased erythroid and myeloid differentiation on treatment with a STAT3 degrader. Furthermore, murine model of venetoclax resistance showed significant reduction in STAT3 & MCL1 on treatment with the STAT3 degrader. Conclusions: Targeting STAT3 and downstream MCL1 is novel strategy in MDS/AML that can spur clinical development of the STAT3 degraders especially given the significant side profile of direct MCL1 inhibitors.
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